EXHIBIT 10.20








                                        December 31, 2002


To the Beneficiary party to the Owner
Trust Agreement referred to below

Ladies and Gentlemen:

         Reference is hereby made to (i) the Owner Trust Agreement dated as of
October 1, 1998, as heretofore amended and supplemented (the "Owner Trust
Agreement"), between Scotiabanc Inc., as beneficiary (the "Beneficiary") and
First Union National Bank, as Trustee and (ii) the Lease Agreement dated as of
October 1, 1998, as heretofore amended and supplemented (the "Lease"), between
the Iron Mountain Statutory Trust - 1998, a Connecticut statutory trust, as
lessor (the "Lessor"), and Iron Mountain Information Services, Inc. (f/k/a Iron
Mountain Records Management, Inc.), as lessee (the "Lessee"). Capitalized terms
used herein without definition that are defined in the Lease are used herein
with the same meaning as in the Lease.

         The undersigned hereby guarantees to the Beneficiary the prompt and
complete payment in cash of its Equity Investment, and the accrued and unpaid
Equity Return thereon, on the Term Termination Date.

                                        IRON MOUNTAIN INFORMATION SERVICES,
                                        INC., as Lessee


                                        By:  /s/ John P. Lawrence
                                             -----------------------------------
                                        Name:    John P. Lawrence
                                        Title:   Vice President and Treasurer

                                        IRON MOUNTAIN INCORPORATED, as Guarantor


                                        By: /s/ John P. Lawrence
                                            ------------------------------------
                                        Name:    John P. Lawrence
                                        Title:   Vice President and Treasurer